共查询到20条相似文献,搜索用时 859 毫秒
1.
I.A. Nyrkova A.N. Semenov A. Aggeli N. Boden 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):481-497
The problem of fibril (fibre) formation in chiral systems is explored theoretically being supported by experiments on synthetic
de novo 11-mer peptide forming self-assembled -sheet tapes. Experimental data unambiguously indicate that the tapes form fibrils of nearly monodisperse thickness ca
. 8-10 nm. Fibril formation and stabilisation are attributed to inter-tape face-to-face attraction and their intrinsic twist,
correspondingly. The proposed theory is capable of predicting the fibril aggregation number and its equilibrium twist in terms
of molecular parameters of the primary tapes. The suggested novel mechanism of twist stabilisation of finite aggregates (fibrils)
is different to the well-known stabilisation of micelles in amphiphilic systems, and it is likely to explain the formation
and stability of fibrils in a wide variety of systems including proteinaceous amyloid fibres, sickle-cell hemoglobin fibres
responsible for HbS anemia, corkscrew threads found in chromonics in the presence of chiral additives and native cellulose
microfibrillar crystallites. The theory also makes it possible to extract the basic molecular parameters of primary tapes
(inter-tape attraction energy, helical twist step, elastic moduli) from the experimental data.
Received 7 May 1999 and Received in final form 15 February 2000 相似文献
2.
J. Chatterjee M. Mitra A.N. Das 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):573-578
A two-site double exchange model with a single polaron is studied using a perturbation expansion based on the modified Lang-Firsov
transformation. The antiferromagnetic to ferromagnetic transition and the crossover from small to large polaron are investigated
for different values of the antiferromagnetic interaction (J) between the core spins and the hopping (t) of the itinerant electron. Effect of the external magnetic field on the small to large polaron crossover and on the polaronic
kinetic energy are studied. When the magnetic transition and the small to large polaron crossover coincide for some suitable
range of J/t, the magnetic field has very pronounced effect on the dynamics of polarons.
Received 1 June 2000 相似文献
3.
4.
Polaronic effects on the energy levels of a double donor impurity in quantum wells in the presence of a magnetic field 总被引:3,自引:0,他引:3
Zi-xin Liu Zhen-jiang Lai Yong-chang Huang Ya Liu Guo-jun Cheng 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):347-350
In the presence of a magnetic field the Hamiltonian of the single or double polaron bound to a helium-type donor impurity
in semiconductor quantum wells (QWs) are given in the case of positively charged donor center and neutral donor center. The
couplings of an electron and the impurity with various phonon modes are considered. The binding energy of the single and double
bound polaron in AlxlGa 1-xlAs/GaAs/AlxrGa 1-xrAs QWs are calculated. The results show that for a thin well the cumulative effects of the electron-phonon coupling and the
impurity-phonon coupling can contribute appreciably to the binding energy in the case of ionized donor. In the case of neutral
donor the contribution of polaronic effects are not very important, however the magnetic field significantly modifies the
binding energy of the double donor. The comparison between the binding energies in the case of the impurity placed at the
quantum well center and at the quantum well edge is also given.
Received 16 February 1999 相似文献
5.
E. Leber S. Barsotti I.I. Fabrikant J.M. Weber M.-W. Ruf H. Hotop 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):125-131
Using a high resolution ( meV) laser photoelectron attachment method, we have studied the formation of (CO 2)
q
− ions (q = 4−22) in collisions of low energy electrons (1−180 meV) with (CO2)
N
() clusters. The previously reported “zero energy resonance”, observed at much larger electron bandwidths, actually consists
of several narrow vibrational Feshbach resonances of the type [(CO 2)
N
−1CO which involve a vibrationally-excited molecular constituent ( denotes vibrational mode) and a diffuse electron weakly bound to the cluster by long range forces. The resonances occur at
energies below those of the vibrational excitation energies of the neutral clusters [(CO 2)
N
−1CO ]; the redshift rises with increasing cluster ion size q by about 12 meV per unit; these findings are recovered by a simple model calculation for the size dependent binding energies.
The size distribution in the cluster anion mass spectrum, resulting from attachment of very slow electrons, mainly reflects
the amount of overlap of solvation-shifted vibrational resonances with zero energy; the cluster anion size q is identical with or close to that of the attaching neutral cluster.
Received 11 January 2000 and Received in final form 10 April 2000 相似文献
6.
Zu Wei Yan Xi Xia Liang 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):531-538
A variational theory is proposed to study the surface states of electrons in a semi-infinite ternary mixed crystal, by taking
the effect of electron-surface optical (SO) phonon interaction into account. The energy and the wave function of the electronic
surface-states are calculated. The numerical results of the energies of the surface states of the polarons and the self-trapping
energies are obtained as functions of the composition x and surface potential V0 for several ternary mixed crystal materials. The results show that the electron-phonon interaction lowers the surface-state
levels with the energies from several to scores of meV. It is also found that the self-trapping energy of the surface polaron
has a minimum at some middle value of the composition x. It is indicated that the electron-phonon coupling effect can not be neglected.
Received 4 January 1999 and Received in final form 7 January 2000 相似文献
7.
N. Gidopoulos S. Sorella E. Tosatti 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):217-226
We study the quantum phase transition between a band (“ionic”) insulator and a Mott-Hubbard insulator, realized at a critical
value in a bipartite Hubbard model with two inequivalent sites, whose on-site energies differ by an offset . The study is carried out both in D=1 and D=2 (square and honeycomb lattices), using exact Lanczos diagonalization, finite-size scaling, and Berry's phase calculations
of the polarization. The Born effective charge jump from positive infinity to negative infinity previously discovered in D=1 by Resta and Sorella is confirmed to be directly connected with the transition from the band insulator to the Mott insulating
state, in agreement with recent work of Ortiz et al. In addition, symmetry is analysed, and the transition is found to be associated with a reversal of inversion symmetry in
the ground state, of magnetic origin. We also study the D=1 excitation spectrum by Lanczos diagonalization and finite-size scaling. Not only the spin gap closes at the transition,
consistent with the magnetic nature of the Mott state, but also the charge gap closes, so that the intermediate state between
the two insulators appears to be metallic. This finding, rationalized within Hartree-Fock as due to a sign change of the effective
on-site energy offset for the minority spin electrons, underlines the profound difference between the two insulators. The band-to-Mott insulator
transition is also studied and found in the same model in D=2. There too we find an associated, although weaker, polarization anomaly, with some differences between square and honeycomb
lattices. The honeycomb lattice, which does not possess an inversion symmetry, is used to demonstrate the possibility of an
inverted piezoelectric effect in this kind of ionic Mott insulator.
Received 21 May 1999 相似文献
8.
The freezing transition of a network model for tensionless membranes confined to two dimensions is investigated by Monte Carlo
simulations and scaling arguments. In this model, a freezing transition is induced by reducing the tether length. Translational
and bond-orientational order parameters and elastic constants are determined as a function of the tether length. A finite-size
scaling analysis is used to show that the crystal melts via successive dislocation and disclination unbinding transitions, in qualitative agreement with the predictions of the Kosterlitz-Thouless-Halperin-Nelson-Young
theory. The hexatic phase is found to be stable over only a very small interval of tether lengths.
Received 4 June 1999 and Revised in final form 1 September 1999 相似文献
9.
N. Chandra S. Sen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(4):457-480
This communication presents a theoretical study of the angular distribution of one or both of the two electrons emitted in
one-photon, one-step double ionization of a linear molecule. Experiments which do or do not detect spin of the photoelectrons
have been considered. Effects of molecular rotation on double photoionization have been studied in both Hund's coupling schemes
(a) and (b) by using parity-adapted states. Selection rules obtained in this paper are very different from those derived earlier
for single photoionization and for Auger decay following the absorption of a photon in a rotating linear molecule. It is shown
that complete specification of the spin-unresolved and of spin-resolved angular distributions of both photoelectrons require,
respectively, three and seven parameters which depend, among other things, on their energies as well as directions of emission.
The approach developed in this paper has been used to analyze spin-unresolved double photoionization in the shell of the molecule. The angular distribution is quite different depending on whether or not molecular rotation has been taken into
account. Also, it is found to change significantly for different rotational transitions. Effects of electron-electron correlation
are clearly manifested even in non-coincident, both rotationally resolved--as well as unresolved--double photoionization.
Received: 7 August 1998 相似文献
10.
R. Granger J.T. Benhlal O. Ndap R. Triboulet 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):429-436
The dielectric function of ZnSe has been deduced from ellipsometric measurements between 20 K and 380 K. is analysed around each critical point with the standard critical point model. The variations of the different parameters
characterising each transition with temperature are presented and analysed. The temperature coefficients of the energies of
the critical transitions are given. is essentially governed by the Coulomb interaction near the fundamental gap. Thanks to the high binding energy of the exciton
and the low spectral width of the ellipsometer, the fundamental state of the exciton is found completely separated from the
first excited states and the continuum at low temperature. In return the strong transition E1 near the L points of the Brillouin zone can be described equally well with a 2D or an excitonic transition.
Received 5 February 1999 and Received in final form 15 June 1999 相似文献
11.
12.
T. Emig T. Nattermann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):525-546
The simultaneous effect of both disorder and crystal-lattice pinning on the equilibrium behavior of oriented elastic objects
is studied using scaling arguments and a functional renormalization group technique. Our analysis applies to elastic manifolds,
e.g., interfaces, as well as to periodic elastic media, e.g., charge-density waves or flux-line lattices. The competition between both pinning mechanisms leads to a continuous, disorder
driven roughening transition between a flat state where the mean relative displacement saturates on large scales and a rough
state with diverging relative displacement. The transition can be approached by changing the impurity concentration or, indirectly,
by tuning the temperature since the pinning strengths of the random and crystal potential have in general a different temperature
dependence. For D dimensional elastic manifolds interacting with either random-field or random-bond disorder a transition exists for 2<D<4, and the critical exponents are obtained to lowest order in . At the transition, the manifolds show a superuniversal logarithmic roughness. Dipolar interactions render lattice effects
relevant also in the physical case of D=2. For periodic elastic media, a roughening transition exists only if the ratio p of the periodicities of the medium and the crystal lattice exceeds the critical value . For p<p
c
the medium is always flat. Critical exponents are calculated in a double expansion in and and fulfill the scaling relations of random field models.
Received 28 August 1998 相似文献
13.
Koga T 《The European physical journal. E, Soft matter》2005,17(3):381-388
The formation of intramolecular micelles in copolymers with periodic sequence, where hydrophobic units (stickers) are periodically placed along the chain, is studied by using multicanonical Monte Carlo computer simulations for an off-lattice bead-rod model in three dimensions. With decreasing the temperature, a transition from random-coil conformations to micelles occurs and flower-type micelles are formed via the transition. The number of stickers forming a micelle core is limited by the excluded-volume effect of loop chains around micelle cores. By this effect, two intramolecular micelles are formed for long polymer chains with 60 bonds via the coil-to-micelle transition. By further decreasing the temperature, we find that another transition, i.e., a micelle-to-micelle transition, takes place. At this transition point, the two intramolecular micelles merge into one micelle. Furthermore, we extend the multicanonical MC method to study elastic properties of single polymer chains with strong attractive interactions under external force fields, and study how the intramolecular micellization affects the elastic property of single polymer chains. 相似文献
14.
J. Cleymans H. Oeschler K. Redlich S. Wheaton 《The European Physical Journal A - Hadrons and Nuclei》2006,29(1):119-121
The present status of the thermal model is reviewed and the recently discovered sharp peak in the K
+/π+ ratio is discussed in this framework. It is shown that the rapid change is related to a transition from a baryon-dominated
hadronic gas to a meson-dominated one. Further experimental tests to clarify the nature of the transition are discussed. In
the thermal model the corresponding maxima in the Ξ/π and Ω/π ratios occur at slightly different beam energies. 相似文献
15.
D. Loison K.D. Schotte 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):735-743
The nature of the phase transition for the XY stacked triangular antiferromagnet (STA) is a controversial subject at present. The field theoretical renormalization group
(RG) in three dimensions predicts a first order transition. This prediction disagrees with Monte-Carlo (MC) simulations which
favor a new universality class or a tricritical transition. We simulate by the Monte-Carlo method two models derived from
the STA by imposing the constraint of local rigidity which should have the same critical behavior as the original model. A
strong first order transition is found. Following Zumbach we analyze the second order transition observed in MC studies as
due to a fixed point in the complex plane. We review the experimental results in order to clarify the critical behavior observed.
Received: 18 February 1998 / Revised: 24 April 1998 / Accepted: 30 April 1998 相似文献
16.
A flow control study of a supersonic mixing layer via NPLS 总被引:1,自引:0,他引:1
The flow control of a supersonic mixing layer was studied in a supersonic mixing layer wind tunnel with convective Mach number
(Mc) at 0.5. The passive control of the mixing layer was achieved by perturbation tapes on the trailing edge of the splitter
plate. The control effects of 2D and 3D perturbation tapes with different sizes were compared. The mixing layer was visualized
via NPLS, and the transient fine structures were identifiable in NPLS images, which were used to analyze the effects of flow
control. The results show that the 2D tapes can enhance the 2D characteristic of the mixing layer, delaying mixing layer transition;
and the 3D tapes can enhance the 3D characteristic of the mixing layer, advancing mixing layer transition. 3D structures of
the mixing layer were visualized, and the H-type Λ vortexes were found with 3D tapes control. 相似文献
17.
18.
J.L. Meunier A. Morel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):341-352
For the first order transition of the Ising model below , Isakov has proven that the free energy possesses an essential singularity in the applied field. Such a singularity in the
control parameter, anticipated by condensation theory, is believed to be a generic feature of first order transitions, but
too weak to be observable. We study these issues for the temperature driven transition of the q states 2D Potts model at . Adapting the droplet model to this case, we relate its parameters to the critical properties at and confront the free energy to the many informations brought by previous works. The essential singularity predicted at the
transition temperature leads to observable effects in numerical data. On a finite lattice, a metastability domain of temperatures
is identified, which shrinks to zero in the thermodynamical limit.
Received 30 March 1999 相似文献
19.
M.S. Li M. Cieplak 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):787-792
The Go model is extended to the case when the non-native contact energies may be either attractive or repulsive. The folding
temperature is found to increase with the energy of non-native contacts. The repulsive non-native contact energies may lead
to folding at T=0 for some unusual two-dimensional sequences and to reduction in complexity of disconnectivity graphs for local energy minima.
Received 10 May 1999 and Received in final form 13 October 1999 相似文献
20.
F.W.S. Lima J.E. Moreira J.S. Andrade Jr. U.M.S. Costa 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):107-110
We investigate the two-dimensional eight-states ferromagnetic Potts model in the Voronoi-Delaunay tessellation. In this study,
we assume that the coupling factor J varies with the distance r between the first neighbors as , with . The disordered system is simulated applying the single-cluster Monte-Carlo update algorithm and the reweighting technique.
We find that this model displays a first-order phase transition if , in agreement with previous recent studies. For and 1.0, a typical second order transition is observed and the critical exponents for magnetization and susceptibility are
calculated.
Received 19 May 1999 and Received in final form 2 June 1999 相似文献